1. Field of the Invention
The present invention relates to an absolute magnetic encoder for generating absolute signals that indicate an absolute rotational position of a servomotor shaft or other rotational body, and more particularly relates to an absolute magnetic encoder capable of generating high-resolution absolute signals without increasing the number of magnetic pole tracks formed on an external peripheral surface of a magnetic drum and increasing the axial length.
2. Description of the Related Art
FIGS. 9A and 9B are a front view and side view showing a configuration of a detection portion of a commonly known absolute magnetic encoder. As shown in the drawings, N tracks, or four magnetic pole tracks 102 to 105 ranging from 20 to 23 are aligned in the direction of a drum axis 101a on the external peripheral surface of a magnetic drum 101 fixed to the motor shaft of the measurement object or another rotational body. Hall sensors or other magnetic sensors 202 to 205 are disposed facing the magnetic pole tracks 102 to 105, respectively. Shown in FIG. 10 are bit signals for each digit obtained from the magnetic sensors 202 to 205 for these digits.
In an absolute magnetic encoder with this configuration, when the number of bits is increased in order to enhance the resolution, the number of tracks increases proportionately and the axial length of the magnetic drum 101 increases as well. This becomes an impediment to reducing the size and weight of a high-resolution absolute magnetic encoder.